Process for the manufacture of polyalkylene terephthalates using zinc amino-triethanolate as transesterification catalyst

ABSTRACT

IN THE PRODUCTION OF FILAMENT- OR FILM-FORMING POLYALKYLENE TEREPHTHALATES BY TRANSESTERIFICATION FOLLOWED BY POLYCONDENSATION, ZINC AMINOTRIETHANOLATE IS USED AS THE TRANSESTERIFICATION CATALYST, PREFERABLY IN COMBINATION WITH THE USE OF BISMUTH AMINOTRIETHANOLAMINE AS THE POLYCONDENSATION CATALYST. MUCH SMALLER AMOUNTS OF THESE CATALYSTS CAN BE USED THAN OF PRIOR ART CATALYSTS, AND THE PRODUCT HAS A HIGH DEGREE OF THERMAL STABILITY.

United States Patent ice Int. Cl. C07c 67/02; C08g 17/013, 17/015 US. Cl. 260-75 Claims ABSTRACT OF THE DISCLOSURE In the production of filamentor film-forming polyalkylene terephthalates by transesterification followed by polycondensation, zinc aminotriethanolate is used as the transesterification catalyst, preferably in combination with the use of bismuth aminotriethanolamine as the polycondensation catalyst. Much smaller amounts of these catalysts can be used than of prior art catalysts, and the product has a high degree of thermal stability.

This invention relates to the manufacture of polyalkylene terephthalates by transesterification followed by polycondensation. It is 'known to prepare polyesters by an ester interchange (transesterification) between a lower alkyl diester of an aromatic dicarboxylic acid, in particular terephthalic acid, and a glycol of formula in which n is between 2 and 10 inclusive, followed by polycondensation. Also this type of polymer can be obtained by direct esterification of the diacid with an alkylene oxide, for example ethylene oxide followed by polycondensation.

In all cases the transesterification, esterification and polycondensation reactions are efiected in the presence of catalysts which serve the purpose of accelerating the reactions and allowing polymers to be obtained which have properties enabling them to be used in the form of filaments, films or moulded articles.

Acetates of metals of groups II and VII of the Periodic Classification of the Elements, especially manganops acetate, are widely employed as transesterification catalysts, but it is necessary to incorporate a relatively high quantity of these to achieve suflicient catalytic effect for the reaction to take place within a fairly short time.

Antimony oxide is the most commonly employed of the polycondensation catalysts, but it has already been found that certain .bismuth compounds have advantages over antimony oxides. In particular, bismuth aminotriethanolate makes it possible, to achieve high speeds of reaction using very small quantities of the metal. However, the resulting polymers are not pure white and have a relatively high yellowness index.

Further, the applicant has already proposed, in US. patent application Ser. No. 593,288 filed Nov. 10, 1966, now Pat. No. 3,475,379, to use triethanolamine as a polycondensation catalyst, optionally in the presence of phos phorous acid as a stabiliser, to give polymers having improved colour and heat stability.

It has now been found that polyesters of improved heat stability, such that the use of phosphorous acid as a stabiliser can be dispensed with, can be obtained by Patented Feb. 16, 1971 using as the transesterification catalyst zinc aminotriethanolate.

Accordingly the invention consists in a process for the production of polyalkylene terephthalates by effecting transesterification between a lower (e.g. C -C alkyl ester of terephthalic acid and a polymethylene glycol having 2-1 0 carbon atoms in the molecule, and subjecting the resulting bis(w-hydroxy-n-alkyl) terephthalate to polycondensation, in which the transesterification step is carried out in the presence of zinc aminotriethanolate as catalyst. The polycondensation stage is preferably carried out using bismuth aminotriethanolate as catalyst, in which case a very high degree of thermal stability in the solid state can be achieved without the use of phosphorous acid. If other polycondensation catalysts, e.g. triethanolamine itself, or even antimony oxide, are used, less advantage as regards heat stability is obtained.

This process makes it possible to prepare polymers having properties (intrinsic viscosity, number of terminal acid groups and softening point) as good as those of polymers prepared in the presence of known catalytic systems, using lower polycondensation temperatures.

Although the amounts of transesterification catalyst and polycondensation catalyst used can vary over a wide range, the superior activity of zinc aminotriethanolate and bismuth aminotriethanolate respectively enables them to be used in amounts considerably smaller than are usual for earlier catalysts. Thus the zinc compound can be used in amount 20 to parts per million, and preferably 40 to 80 parts per million (reckoned as zinc), and the bismuth compound in amount 5 to 200, and especially 5 to 50, parts per million (reckoned as bismuth), both based on the weight of the ester of terephthalic acid (reckoned as dimethyl terephthalate).

The heat stability of the polyesters obtainable in accordance with the invention (evaluated from the change in intrinsic viscosity and in the number of terminal groups after 24 hours at C.) is as good in the absence of stabilisers as that of polymers previously prepared in the presence of derivatives of the phosphorous oxyacids, in particular phosphorous acid, which are usually employed as stabilisers.

The polymers obtained can be formed into shaped articles, elg. filaments or films, which have properties comparable to those of filaments or films obtained from the best polymers prepared by the processess already known, especially as regards yellowness index, brightness, tensile strength and elongation at break.

The following examples illustrate the invention.

EXAMPLES 1-3 Transesterification is first carried out in a 10 litre glass flask between 3,298 g. (17 mols) of dimethyl terephthalate and 2,635 g. (42.5 mols) of ethylene glycol in the presence of a transesterification catalyst. After distilling ofl the methanol and the excess ethylene glycol the reaction mixture is transferred to a 7.5 litre stainless steel autoclave provided with a stirrer system. The polycondensation catalyst and 0.5% by weight, relative to the polymer, of titanium oxide, both suspended in ethylene glycol, are then added to the reagents which are at a temperature of about 230 C. The reaction mixture is then heated at 250 C. at atmospheric pressure with stirring, whilst distilling oif ethylene glycol. Heating is thereafter continued at a temperature rising from 250 C. to the temperature T chosen for the polycondensation whilst progressively lowering the pressure in the autoclave to about 2.5 mm. of mercury. Finally, in a last stage, termed hereinafter the polycondensation stage, the pressure is further lowered to 0.2 mm. of mercury Whilst keeping it possible to work at a lower temperature than is necessary with the comparison systems without increasing the TABLE III Polycondensation phase Polymer properties Filament properties After 24 hrs. heat treatment at 185 C.

Yellow- Bright- Yellow- Bright- Tensile Elon- Example Temp., G.T. P.R., AG.T. ness ness, ness ness, strength, gation, No. 0. Duration V.I. l COOH 5 C. AV.I. COOH index percent index percent gJden. percent 280 2 hours 30 mills. 0. 67 26 262. 5 0. 08 14 11 51. 2 10. 5 83. 2 5. 48 19. 2 287 do 0. 66 35 261.2 0. 04 2 1 45 6 85. 5 5. 33 20.2 287 do 0. 68 38 261. 9 0. 07 6 6 48. 5

See footnotes at end of Table IV.

duration of the polycondensation. The properties of the 15 polymer and of the filaments remain similar.

The catalyst systems used were:

Example Trans esterification Polycondensation 4 Manganous acetate Bismuth aminotriethanolate 5 Zine amino-triethanolate- Do.

Polymers were prepared in a 2,000 litre autoclave from TABLE I Trans-esterification Polyeondensation Polycondensation catalyst catalyst stage HaPOZ Nature Amount 1 Nature Amount 1 Content Temp, 0. Duration Example No.:

1 i ATZn 54 ATB13 50 280 1 hour 17. Manganous 109 511203 338 134 287 1 hour 43.

acetate. 3 Calcium 179 SbzOa 338 134 287 1 hour 40.

acetate.

1,150 kg. of dimethyl terephthalate and 720 kg. of ethylene glycol by the general method of Example I. Table IV summarises the working conditions and the results ob tained and clearly shows the advance achieved by the in- Polymer properties Filament properties After 24 hrs. heat treatment at Diethyl- C. en

glycol Yellow- Bright- Yellow- Bright- Tensile Elon- Example G .T. I.R., AG.T. content, ness ness, ness ness, strength, gation, 0. V 1. COOH 6 C. AV I COOH percent index percent index percent g./den. percent See footnotes at end of Table IV.

Nora-The principle of the determination is explained by O. B. Edgar and E. Ellery, J. Chem. Soc., 2,633-2,638, 1952.

It will be seen from this table that when zinc aminotriethanolate is used as the transesterification catalyst and bismuth aminotriethanolate as the polycondensation vention.

The catalytic system of the present invention produces polymers of improved heat stability, shown by the small TABLE IV Polymer properties Transesterification Polyeondensation Polycondensation After 24 hrs. heat catalyst catalyst stage treatment at 185 0.

Yellow- Brl ht- Exanlplo Temp, G- P- AG.T. ness hiss, No. Nature 1 Amount 1 Nature 1 Amount 1 0. Duration V.I. 4 COOH C. AV.I. COOH index percent 4 Mangarous 109 ATBi 20 287 4hours. 0.66 262 0.17 115 22 53 &

aceta e. AtZn 54 AIBi 3 283 4 hrs. 66 45 261. 3 0. 08 12 13 45 3 4O 1111I1S.

1 Pants by weight per million of zinc, manganese, calcium, bismuth, antimony 0r phosphor us relative .to dimethyl 'terephthalate.

2 ATZnzZinc aminotriethanolate. 3 ATBizBismuth aminotriestlinnolate.

*V.I.:Intninsic viscosity determined at 25 C. on o. 1% weight/volume solution of polymer in o-chlorophenol. Gll. COOH=Number of terminal 'COOH groups per ton of polymer.

G P.R.:Sofitening point measured by penetrometric method.

catalyst, the viscosity properties of the polymer and the properties of the filaments remain similar to those achieved with the catalytic systems used by way of comparison 70 while it is unnecessary to incorporate phosphorous acid. Polymers were also produced in a 300 litre autoclave using the same catalyst systems.

The results are summarised in Table III, which again reduction in intrinsic viscosity and increase in the number of carboxyl terminal groups after heat treatment.

We claim:

1. A process for the manufacture of filamentor filmforming polyalkylene terephthalates of improved heat stability which includes the steps of effecting transesterification between a lower alkyl ester of terephthalic acid shows that the catalytic system of the invention makes and a polymethylene glycol having 2-10 carbon atoms in the molecule, followed by polycondensation, in which 20 to 150 parts by weight of zinc in the form of a zinc aminotriethanolate are used as a catalyst for the transesterification step, per million parts by weight of lower alkyl ester of terephthalic acid, reckoned as dimethyl terephthalate.

2. A process according to claim 1, in which 5 to 200 parts by weight of bismuth in the form of bismuth aminotriethanolate are used as a catalyst in the polycondensation step per million parts by weight of lower alkyl ester of terephthalic acid, reckoned as dimethyl terephthalate.

3. A process according to claim 1, in which the ester of terephthalic acid is dimethyl terephthalate, and the glycol is ethylene glycol.

4. A process according to claim 2, in which the ester of terephthalic acid is dimethyl terephthalate, and the glycol is ethylene glycol.

5. A process according to claim 2, in which 40 to 80 parts by weight of zinc in the form of zinc amino-triethanolate and 5 to 50 parts by weight of bismuth in the form of bismuth aminotriethanolate are used, both per million parts by weight of the lower alkyl ester of terephthalic acid, reckoned as dimethyl terephthalate.

References Cited UNITED STATES PATENTS 3,405,096 10/1968 Chambion 26075 WILLIAM H. SHORT, Primary Examiner L. P. QUAST, Assistant Examiner U.S. Cl. X.R. 

